Google is adding 41 new features to its Google+ social network on Wednesday, including a richer interface that works better on mobile devices and some major enhancements to photo sharing.

There's little Google can do to improve one essential feature, however – the number of active users on the service.

Speaking at the company's I/O event in San Francisco Wednesday, senior vice president Vic Gundotra said "hundreds of millions" of people have joined the service, but he didn't specify how many were active users. Facebook has just over a billion monthly active users.

Top of the list of new features on Google+ is a redesigned social stream that, on devices with wider screens, can show up to three columns of posts from friends and colleagues. Posts including photos and videos can span multiple columns to give the interface a richer appearance, said Gundotra. And the number of columns can be narrowed to a single column for viewing on mobile devices.

Also new is automatic hashtagging. Gundotra used the example of a post about San Francisco Giants player Buster Posey that didn't originally have hashtags. Google automatically adds tags to the photos, one on the team and one on the player.

It's part of an effort to add more depth to Google+, so that users can drill down and explore topics that interest them. Clicking on the hashtag will reveal related content on the social network that Google has also tagged, with an emphasis on content from friends.

Social networks today are "flat" and like reading "a never-ending newspaper," Gundotra said. "It's almost impossible to go deeper on a topic or interest you might have."

Google tags the images using image recognition. It gave another example of a photograph of the Eiffel Tower, which has been automatically tagged in a post. Clicking on the tag revealed more information about the Eiffel Tower and Paris.

Google said users will have the option to turn off the automatic tagging feature, from either individual images or all their images.

The new interface will be launched starting Wednesday.

Group chats that last for weeks

Google is also enhancing Hangouts so that they become ongoing conversations between people in circles – a sort of group chat that runs for days or weeks between friends and family members.

But perhaps the biggest change comes in the way the service will handle photos. Google has added several new features to automatically enhance photos uploaded by users, including tools that automatically soften wrinkles on faces and reduce "noise" in grainy photographs.

Google says the features are comparable to those in photo editing software or specialized modes on cameras, but are done by Google servers.

Given a file of hundreds of vacation photos, Google will also choose the best ones automatically, based on factors like blur and whether people are smiling, Gundotra said. It has even used machine learning to detect esthetics, such as a good composition.